It is well known that fusion type phase change materials are capable of storage and release of large amounts of thermal energy. While fusion type phase change materials change phase from a solid to a liquid, they are limited in the amount of thermal energy they can store and release. Water, which has the capability to change from a liquid to a vapor and then from a vapor to a liquid (i.e., referred to herein as a water vapor phase change cycle), is a much more effective phase change material surpassing the heat accumulation and heat releasing capacity of fusion type phase change materials many times over. In this regard, water has exceptional thermal energy storage and thermal energy transferring properties when changing phases from a liquid to a vapor and then from a vapor to a liquid. Water used as a phase change material is therefore very useful for the thermal energy conditioning of a heat sink mass of a building structure when a method and apparatus configured for controlling the phase change of water within a heat sink mass defining an interior space or interior space partitions of a building structure is configured for climatically conditioning of the heat sink mass and for displacing thermal energy (i.e., heat) from the heat sink mass to a space outside of the interior space of the building structure.
Traditionally evaporative cooling systems have been used with great success and with very low energy consumption in climate zones that are hot and dry. However, in climate zones that are hot and humid, evaporative cooling and indirect evaporative cooling systems have had only limited success with respect to compressed gas cooling systems. Desiccant air drying in combination with evaporative cooling have also been tried with some success, but require large systems to condition the total cubic area within a living space of a building structure. Similarly, previous approaches for providing acceptable comfort levels within a living space of a building structure utilizing water evaporation systems in hot humid climate zones have been marginally successful primarily because the focus of such previous approaches has been the conditioning of the air within the living space of the building structure. In this regard, such known climatic control systems have not been successful at providing thermal comfort in a building structure in hot and humid climates in a manner that utilizes low energy consumption.
Some other previous approaches for providing a thermal comfort range for humans within a living space of a building structure rely on a method of thermal conditioning of a heat sink mass of a building structure (e.g., walls and/or floors thereof). Such thermal conditioning of the heat sink mass is typically performed by circulating cooling or heating fluids through piping imbedded within the heat sink mass, thereby either circulating heated fluid through piping in the heat sink mass and then outwardly radiating heat to the occupants within the living space or by circulating cooled fluid through piping in the heat sink mass. In the case of circulating the cooled fluid, heat transferred into the fluid from the living space is then displaced to a space outside of the building structure generally through a forced air heat exchanger, thereby removing heat from the heat sink mass. Transferring thermal energy through a water circulating system within a heat sink mass of a building structure for heating and cooling is very efficient, but is not very cost effective in that the cost of the additional materials such a piping, pumps and heat exchangers for cooling and heating fluids increase costs of heating and cooling the building structure.
Two forms of heat are relevant in air conditioning: sensible heat and latent heat. When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat. All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat. The heat that causes these changes is called latent heat. Latent heat is thermal energy released or adsorbed during a phase-change of a chemical substance such as water; latent heat of vaporization/condensation (Lv) is the energy released or adsorbed in a phase-change from a liquid to vapor or vapor to a liquid. The reaction is exothermic or endothermic depending on the direction of the phase change Latent heat of vaporization is the quantative thermal energy required to change water from a liquid phase to a vapor phase without changing the temperature of the substance for example, water remains at 100° C. while boiling. The additional heat added while boiling the water is transferred into the phase change of vaporizing water. For this reason the temperature of the boiling water stays at a constant temperature although additional heat is being added to the boiling water. Heat of condensation is exothermic therefore the thermal energy released from the vaporized water at the phase change of the water vapor to liquid water is released to the surrounding environment. The quantative thermal energy transferred during the phase change of water from a liquid to a vapor and from a vapor to a liquid is equal. The transfer of this thermal energy from phase to phase is at least one of a preferred means of transferring thermal energy to and from the heat sink mass of the present discloser. In the present discloser cycled vapor pressure differentials at ambient temperatures promote the change of phase of water. When water in a liquid phase within the heat sink mass of the building structure is caused to evaporate from the heat sink mass of the building structure to the lower pressure of a circulating dry air stream, the sensible temperature of the heat sink mass is reduced to a lower sensible temperature. In the present discloser the quantitive thermal energy required for the vaporization of the liquid water is transferred out of the heat sink mass of the building structure and the liquid water mass within the heat sink mass to the vaporizing water and thereby conditions the heat sink mass to a lower sensible temperature, this thermal energy is carried away within the air of the closed loop circulating air stream and then out to a space outside of the building structure. Appreciating these properties of the phase change of water from a liquid to a vapor and then from a vapor to a liquid is fundamental to understanding at least one of the preferred means by which thermal energy is transferred into/out of the heat sink mass of the building structure of this present discloser.
Adobe building materials (e.g., blocks) and similarly types of building materials (e.g., compressed earth blocks, rammed earth, cob) are well known for their capacity to provide thermal comfort for the occupants within a living space of a building structure made therefrom. These types of building materials, which function as heat sink masses and a hygroscopic phase change media, typically comprise a mixture of sand, gravel, agricultural plant fiber and clay and, if desired, material binders. Adobe building materials and the like also comprise porous compositions such as clay and a wide range of open pore structure sizes formed between particles of the combined compositions. The clay composition comprises a negative electrostatic attraction (referred to as cation exchange capacity) to the positive ions of water. Adobe and other similar materials can therefore be considered as a building material that has elevated hygroscopic properties. In this regard, these types of building materials form a composite material that is capable of accumulating and transferring sensible and latent heat, through the transmission of water vapor, within/through the heat sink mass of the building structure and within the water mass condensed therein. The heat sink mass of the building structure comprise sufficient mass for supporting thermal energy for extended periods of time and thereby extending periods of time between activation of the cycled conditioned air streams.
Adobe building materials, which are a type of heat sink mass (i.e., adobe heat sink mass), provide a composition that supports phase change of liquid water to water vapor and from water vapor to liquid water into/out of a heat sink mass made from such building materials. For example, negatively charged clay particles within an adobe heat sink mass attract water vapor (being bipolar) through an electrostatic attraction from the surrounding environment comprising high humid conditions typically in night-time and early morning hours when cooler temperatures are present. As ambient air is cooled during the night and early morning hours, humidity increases and water vapor within the surrounding air is diffused into the porous adobe heat sink mass through adsorption resulting from a water vapor pressure imbalance between the relatively dry adobe heat sink mass and the ambient climatic air conditions, thereby causing water vapor to be diffused into the relatively dry, negatively charged clay particles of the adobe heat sink mass, forming an electrostatic attraction between the clay particles of the adobe heat sink mass and the positive ions of water and, thus, water vapor is changed to a liquid within the clay particles and porous structures of the adobe heat sink mass. The resulting phase change is exothermic and therefore thermal energy is released to the surrounding environment. During the less humid warm daytime hours a vapor pressure differential is formed between the condensed liquid water contained within the adobe heat sink mass and the dry daytime air, liquid water within the adobe heat sink mass receives thermal energy through solar radiation and other radiation sources and is changed back to a vapor through a process of evaporation, thereby vaporizing the liquid water mass within the adobe heat sink mass and begins diffusing water vapor out of the porous structures of the adobe heat sink mass to the surrounding environment along with the associated thermal energy accumulated within the adobe heat sink mass and the condensed liquid water mass within the adobe heat sink mass thus, lowering the sensible heat of the adobe heat sink mass through evaporative cooling, providing a cooling effect of nearly 1.000 BTUs of thermal energy removed from the heat sink mass and the liquid water mass within the adobe heat sink mass for every pound of water evaporated. Therefore, compositions of adobe heat sink mass in combination with natural climatic changes between cool moist night air and hot dry day time air provide the combined conditions for changing phases of water from a vapor to a liquid and from a liquid to a vapor within the adobe heat sink mass, thereby naturally and passively providing thermal conditioning of the adobe heat sink mass of a building structure. In this regard, adobe building structures are known to be warm during the cool of night and cool in the heat of day
While this climatic conditioning of a living space within a building structure made using adobe heat sink masses using the natural method of heating and cooling a building structure works very well, it has limitations based on the limited natural cycles of cool, humid evenings and warm dry days. The limiting factor in the effectiveness of this climatic conditioning is the limited number of thermal conditioning cycles transpiring in a given time frame (e.g., typically one cycle per day).
Therefore, an approach for providing thermal comfort (i.e., climatic conditioning) within an interior space of a building structure in multiple climate zones including hot and humid climates using very low energy consumption and overcoming limitations associated with naturally occurring limited number of thermal conditioning cycles transpiring over a day would be beneficial, desirable and useful.